Variable bandwidth automatic gain control

ABSTRACT

Provided is automatic gain control (AGC) in which a feedback filter has a parameter that is changed based on information regarding data-packet boundaries. In one representative embodiment, the bandwidth of the filter temporarily is increased, or the time constant of the AGC filter temporarily is decreased, within a vicinity of each actual or potential packet boundary.

Priority is claimed to U.S. Provisional Patent Application Ser. No.60/735,466, filed on Nov. 9, 2005, and also titled “Variable BandwidthAutomatic Gain Control”, which application is incorporated by referenceherein as though set forth herein in full.

FIELD OF THE INVENTION

The present invention pertains to automatic gain control in adata-packet-based communication receiver, such as a receiver in awireless CDMA 1×EVDO system or a receiver in a wireless 802.11 network.

BACKGROUND

FIG. 1 illustrates a block diagram of a conventional automatic gaincontrol (AGC) system 10. AGC is a signal-processing technique that isused, inter alia, by a communication receiver to dynamically compensatefor widely varying channel gains encountered in various wireless andwire-line transmission channels 12. In a conventional approach, the AGCblock 10 forms a loop by estimating 16 the signal strength of thereceived signal at the output of a variable-gain block 14, filtering 18the estimate to smooth out the instantaneous variations (e.g., due tonoise), comparing the results to a specified target value 19, and thenchanging the gain in variable-gain block 14 in a feedback fashion in anattempt to maintain the received signal strength at the specified targetvalue 19. The gain-adjusted signal is-then subsequently processed 20 todecode the information embedded in the received signal.

The loop filter 18 is usually designed to have a fixed time-constantthat is chosen to achieve a balance between the contradictoryrequirements of broader loop bandwidth for faster AGC loop tracking ofthe input signal strength variations (due to changes in the gain intransmission channel 12) and narrower bandwidth to reduce noise. Anydifference between the filtered estimate and the specified target valueis assumed to have been caused by a change in gain in the transmissionchannel 12 from the last measurement. Accordingly, this difference isused to control the gain in block 14, in a feedback fashion. Underappropriate circumstances, this feedback process ensures stable trackingand compensation for changes in the channel gain in an iterative manner.

However, the present inventors have discovered that the fixed bandwidthof the conventional receiver AGC loop filter 18 typically is optimizedfor a received signal that is continuous in nature and does not workvery well with a received signal that is discontinuous in nature (e.g.,packet transmissions) or has step changes in its strength. This isbecause of the fixed time-constant of the AGC loop-filter, which istypically selected to keep the loop bandwidth narrow so as to keep thenoise in the signal strength estimates 16 from causing spurious jumps inthe receiver gain 14 being controlled by the AGC loop 10. To be able totrack such step changes in received signal strength with conventionalAGC, the AGC loop bandwidth ordinarily would have to be kept larger, butthat approach generally results in increased noise through the AGC loop10.

SUMMARY OF THE INVENTION

The present invention addresses this problem by providing automatic gaincontrol (AGC) in which a feedback filter has a parameter that is changedbased on information regarding data-packet boundaries. In onerepresentative embodiment, the bandwidth of the filter temporarily isincreased, or the time constant of the AGC filter temporarily isdecreased, within a vicinity of each actual or potential packetboundary.

In a more specific embodiment, the present invention addresses theabove-referenced problem by widening the AGC loop bandwidth to make itperiodically faster (e.g., at, or within a vicinity of, the actual orpotential data-packet boundaries for discontinuous signals) so as toallow faster tracking of any step changes in the input signal strength.At all other times, the AGC loop bandwidth is kept narrow enough tooffer sufficient filtering of the noise-induced variations in the inputsignal strength. Thus, by keeping the AGC loop bandwidth sufficientlynarrow (e.g., slower tracking) for most of the time and broadening itperiodically (e.g., faster tracking), AGC according to the presentinvention can track discontinuous changes in signal strength withoutsacrificing noise performance of the AGC loop for most of the durationof the signal. In short, by virtue of the foregoing arrangement, itoften is possible to more accurately accommodate changing power levelsat the transmission side, while simultaneously suppressing unnecessarynoise in the AGC loop.

The foregoing summary is intended merely to provide a brief descriptionof the general nature of the invention. A more complete understanding ofthe invention can be obtained by referring to the claims and thefollowing detailed description of the preferred embodiments inconnection with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional automatic gain controlcircuit.

FIG. 2 is a block diagram of an automatic gain control circuit accordingto a representative embodiment of the present invention.

FIG. 3 illustrates a portion of a transmission timeline for data-packetcommunications.

FIG. 4 illustrates the gain applied in a representative conventional AGCloop in response to the input signal shown in FIG. 3, assuming aconstant gain in the transmission channel.

FIG. 5 illustrates a timeline for filter-parameter adjustment accordingto a first representative embodiment of the present invention.

FIG. 6 illustrates the gain profile that results in response to theinput signal shown in FIG. 3 when temporarily increasing the bandwidth,or reducing the time constant, of the AGC filter starting at thebeginning of each data slot, according to the first representativeembodiment of the present invention, again assuming a constant gain inthe transmission channel.

FIG. 7 illustrates a timeline for filter-parameter adjustment accordingto a second representative embodiment of the present invention.

FIG. 8 illustrates the gain profile that results in response to theinput signal shown in FIG. 3 when temporarily increasing the bandwidth,or reducing the time constant, of the AGC filter according to the secondrepresentative embodiment of the present invention, again assuming aconstant gain in the transmission channel.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 2 is a block diagram of an automatic gain control system 30according to a representative embodiment of the present invention. Aswith the conventional AGC system 10 shown in FIG. 1, the strength of asignal 13 received through a transmission channel 12 is modified invariable gain block 14. In this regard, block 14 may be a digital oranalog component and may function as an attenuator, an amplifier orboth. The strength (e.g., magnitude or power) of the gain-adjustedsignal 31 is then estimated in block 16. The resulting strength-estimatesignal 32 is provided to filter 18, which filters it and then comparesit to a specified target strength 19 or, correspondingly, which comparesthe strength-estimate signal 32 to the specified target strength 19 andthen filters the comparison. In either event, a control signal 33 isgenerated and is used to control the gain of block 14. Thus, the AGCloop permits tracking of changes in the gain of the transmission channel12 while simultaneously filtering out noise. The gain-controlled signal31 is then subject to subsequent processing 20 to decode the informationin the received signal 13.

As noted above, the transmission channel 12 may be wireless orhardwired; for instance, in representative embodiments transmissionchannel 12 is a wireless link in a code division multiple access (CDMA)system (e.g., using 1×EVDO protocols) or a wireless link in an IEEE802.11 system (e.g., 802.11a, 802.11b or 802.11g). Also, it should benoted that FIG. 2 provides only a high-level block diagram illustratingthe operation of the AGC system 30. Accordingly, various components,such as frequency-shifting components, are not shown in FIG. 2.

The general purpose of AGC loop 30 is to provide processing block 20with a signal having an average strength that is as close as possible tothe specified target signal strength 19. Accordingly, filter block 18generates a comparison (c) between the estimated signal strength (e) andthe target signal strength 19 (t) and then filters the comparison, i.e.,f(c). In practice, the comparison signal generally will be the simpledifference between the estimate and the target, i.e., c=e−t (although itinstead could be a ratio or any other comparison measure). In addition,if we assume that the filter 18 is linear, then f(c)=f(e)−k, wherek=f(t) is a constant. Moreover, even if the filter 18 is nonlinear, if tis a constant then f(c) generally can be implemented as f′(e). That is,in either case only the actual estimated signal strength 32 need befiltered.

Accordingly, references herein to filtering the comparison signal alsoare intended to cover implementations where the filtering function is infact only applied to the estimated signal strength, as well asimplementations where the filtering function is first applied to theestimated signal strength and then the filtered signal is compared tothe target strength 19, with all of the foregoing implementationstypically being equivalent to each other.

One difference between the AGC loop 30 of the present invention and aconventional AGC loop 10 is the present invention's additional feedbackof information 35 regarding the timing of data-packet boundaries. Morespecifically, the present invention pertains to communications systemsin which data are transmitted in discrete packets. Accordingly, discretedata-packet intervals exist. The communication protocol defines aspecific arrangement of slots, with each data packet occupying aninteger number of data slots. That is, a slot is a time unit duringwhich a data packet (or a portion thereof) can be transmitted. A datapacket can be transmitted in a single slot or in multiple slots.Accordingly, the slot boundaries are the actual or potential data packetboundaries. If a data packet is available for communication at thetransmitter during a particular slot, then that data packet (or aportion of it) is transmitted during the corresponding slot. Otherwise,nothing is transmitted during the subject slot. The resultingtransmission pattern is discontinuous, with transmission during discreteperiods of time.

An example of a data-packet transmission timeline 50 is shown in FIG. 3.In this example, an arrangement of equally spaced contiguous data slots51 is defined. Slots 51 can be divided into slots 52, during which adata packet (or a portion thereof) is transmitted, and slots 54, duringwhich no data are transmitted. Data packets (or portions thereof) oftenwill occupy multiple data slots 52, followed by periods of one or moreslots 54 in which no transmission occurs. Four contiguous data slots56-59 are separately identified in FIG. 3 for use as examples in thefollowing discussion.

In response to the specific transmission 50 shown in FIG. 3, andassuming a constant gain in the transmission channel 12, a conventionalAGC loop (e.g., loop 10) having a long time-constant relative to theduration of a single data-packet interval might set the gain of block 14according to the profile 70 shown in FIG. 4. Specifically, due to thebuilt-in relatively slow response of filter 18, the gain declinesrelatively slowly when data packets are being transmitted (in responseto the increased power, which is interpreted as a change in the gain oftransmission channel 12) and increases at a similar rate when no datapacket is being transmitted. The average gain depends upon thepercentage of the total number of data slots 51 in which a data packetis transmitted (i.e., the total number of data slots 52 divided by thesum of the total number of data slots 51, which include data slots 52and data slots 54). In other words, the gain typically will not reachthe optimal level for data packet transmission, but instead will bebiased somewhat higher, with the precise level being dependent uponaverage transmission frequency. Similarly, the gain typically will notreach the optimal level when no data packet is transmitted, but insteadwill be biased somewhat lower, again with the precise level dependentupon the average transmission frequency.

In order to address this problem, the present invention uses thedata-packet boundary information 35 that is fed back from the subsequentprocessing section 20 in order to adjust at least one of the parametersof AGC filter 18. Thus, referring back to FIG. 2, during the course ofthe subsequent processing 20, packet boundary information 35 isgenerated in the normal course of decoding the information in thereceived signal 13. In the present embodiment, the received signal 13 isa synchronous data signal and so the data slots 51 occur at fixedregular intervals. Once the receiver processing section 20 synchronizesto the timing of the received signal 13, the data slots 51 typically areknown for the entire communication session.

Information 35 regarding where the data-packet boundaries occur is thenfed back for use by filter 18. In practice, some adjustment may be madeto the data-packet boundaries, as such boundaries are identified insubsequent processing section 20, in order to account for thesignal-propagation delay that occurs between the receiver portion 30 andthe subsequent processing section 20 of the subject device.

In any event, a filter-parameter adjustment module 37 uses the packetboundary information 35 to adjust at least one of the parameters offilter 18. In a first representative embodiment of the invention, module37 temporarily increases the bandwidth, or reduces the time constant, offilter 18 at the beginning of each data slot 51, as shown in FIG. 5.Referring to FIG. 5, at the beginning of each data slot 51 a parameterof the filter 18 is changed for a specified period of time 81 and thenis changed back to the default value for the remainder 82 of the dataslot 51. In the present embodiment, the data slots 51 have a constantfixed duration and the specified period of time 81 also is constant andfixed.

Typically, the AGC filter 18 is a digital filter. Accordingly,parameter-adjustment module 37 typically need only directly alter thefilter's parameters, e.g., the weighting profile applied to a sequenceof samples within a moving window, in order to effect the foregoingchange. In alternate embodiments, one filter is used for time period 81and an entirely different filter is used for time period 82. However,even in such alternate embodiments, a wider bandwidth (or shorter timeconstant) is in effect during time period 81 than during time period 82.

As indicated above, the temporary change in the parameter(s) of filter18 preferably permits the AGC loop 30 to quickly adjust to a transitionfrom a “no data transmission” slot 54 to “data transmission” slot 52, orfrom a “data transmission” slot 52 to a “no data transmission” slot 54.A transition of either type is referred to herein as a “transmissionboundary” or a “data-packet boundary”.

In order to adjust to a transmission boundary, the magnitude of thechange in the time constant (or bandwidth) of filter 18 can be tradedoff against the duration of the change interval 81 to achieve thedesired result. Generally speaking, adjusting over a relatively shortperiod of time 81 will maximize the amount of time at which the gain iscorrectly set, while adjusting over a relatively longer period of time81 will reduce noise that is introduced during the adjustment period 81and, accordingly, the total amount of noise admitted.

FIG. 6 illustrates the gain profile 100 that results when temporarilyincreasing the bandwidth, or reducing the time constant, of filter 18 atthe beginning of each data slot 51. As shown, because of the fastertracking during the beginning 81 of each data slot 51, the gain is ableto reach the level that is appropriate for the transmission (or lack oftransmission) very quickly. The result is that more optimal gainsettings are achieved, i.e., higher gains when no signal is beingtransmitted and lower gains when a signal is being transmitted, ascompared to the gain profile 70 that would be achieved by a conventionalAGC loop 10. At the same time, because the time-constant (or bandwidth)is only adjusted for a fraction of the total timeline in the preferredembodiments of the invention, less noise typically is admitted than ifthe filter 18 were designed so as to provide uniformly fast tracking.

It also should be understood that in certain protocols the slots used totransmit a single data packet are not contiguous. For example, in awireless CDMA 1×EVDO system a 4-slot data packet might be transmitted atslots x, x+4, x+8 and x+12. For ease of illustration only, the followingdiscussion assumes that the slots for a data packet are contiguous.However, in many embodiments this will not be the case, and the presentinvention is intended to encompass both contiguous and non-contiguouspackets, as well as fixed-length and variable-length packets.

The foregoing embodiment of the invention concerns a relatively simpleadjustment technique in which the parameter of filter 18 is adjusted atthe beginning of each data slot 51. In alternate embodiments, evenbetter results can be achieved if more information is availableregarding the true data-packet boundaries. For example, in a wirelessCDMA 1×EVDO system a single data packet can be 1, 2, 4, 8 or 16 dataslots long, with each data slot being 1.66667 ms (milliseconds) induration, and with the preamble of each data packet (which occurs in thefirst slot of the packet) specifying the packet's actual length.Accordingly, once the preamble is decoded (in subsequent processingblock 20) the true end of the current data packet is known. Thisinformation preferably is fed back, together with information regardingthe boundaries for the data slots 51, as packet boundary information 35.

The result is illustrated in FIG. 7. As shown, the bandwidth of filter18 temporarily is increased (or the time constant decreased) at thebeginning 81 of data slot 56. When the information from data slot 56 isdecoded in processing block 20 a determination is made that thetransmitted data packet is two data slots long. Accordingly, when thisinformation 35 is fed back, adjustment block 37 knows that the bandwidthof filter 18 need not be increased (or the time constant decreased)during any portion of data slot 57, so that the default filterparameters 82 are applied during all of data slot 57. Until the nextmulti-slot data packet is received, adjustment block 37 then continuesto adjust the parameter of filter 18 at the beginning 81 of eachsubsequent data slot 51 (including data slots 58 and 59, as shown inFIG. 7).

As shown in FIG. 8, the resulting theoretical gain profile 100, assumingno noise or change in the gain of transmission channel 12, is identicalin this embodiment to the gain profile 100 of the previous embodimentdiscussed above (shown in FIG. 6). The main difference is observed whenthe effects of noise are taken into consideration. In that case, theshortened period of time during which the increased bandwidth is ineffect (e.g., no period 81 for data slot 57 in the example of FIG. 7)means that less noise typically will be admitted.

More generally, it is preferable to include as much information aspossible (i.e., as available) regarding the data-packet boundaries inthe information 35 that is fed back for use in adjusting the bandwidth,time constant or other parameter(s) of filter 18. By doing so, it oftenwill be possible to reduce the amount of time during which filter 18 ismore sensitive to noise, thereby further reducing the overall level ofadmitted noise.

The extension to non-contiguqus data packets is straightforward. Oncethe first slot 52 has been decoded, the locations of the other slots 52making up the data packet are known. If the transmission statuses of anytwo data slots 51 are known (i.e., whether they are transmission slots52 or non-transmission slots 54), then it is easily determined whether atransmission boundary exists between them. If a transmission boundarydoes in fact exist or if it is unknown whether a transmission boundaryexists, then the parameter(s) of the filter 18 preferably are adjusted(e.g., by increasing the bandwidth) for a period of time 81 within aproximity of the beginning of the second such data slot 51. On the otherhand, if it is known that a transmission boundary does not exist, thenpreferably no such adjustment interval 81 is used during the second ofthe two data slots 51 (i.e., the default filter parameters aremaintained for the entirety of the second data slot 51).

It is noted that the foregoing discussion generally focuses on a singlereceived signal. However, it often will be the case that the receivedradio signal 13 is in fact an aggregate of multiple signals frommultiple different transmitters, with each transmitter operating on adifferent channel (e.g., a different code channel in a CDMA system). Ifall of the transmitters are synchronized to the same timing pattern,i.e., all have the same data-slot boundaries, then implementation of thefirst embodiment discussed above generally can proceed in the samemanner as if there were only a single transmitter.

However, in such a case, rather than considering only a single binarytransmission boundary (from transmit to no-transmit or vice versa) itgenerally will be the case that at each data slot 51 there will be aprobability distribution for the change in the transmission power,corresponding to the probabilities that the various transmitters will betransitioning from transmit to no-transmit or vice versa. Accordingly,the selection of the amount in the increase in the bandwidth (orreduction in the time constant) of the filter 18 and the selection ofthe duration 81 of the change may be made: to accommodate the expectedabsolute worst-case change in received signal power, to accommodate theaverage expected change in received signal power, or to accommodateanything in between (e.g., the expected worst-case change over 1, 2, 3,4 or 5 standard deviations, so that for some expected percentage ofdata-packet boundaries the change in received signal power will be toogreat to be fully tracked during the temporary period 81 of fastertracking).

On the other hand, if the timings of the various transmitters are notsynchronized with each other, or if the second embodiment discussedabove is being implemented, then it is possible to adjust theparameter(s) of filter 18 for a specified amount of time 81 after thebeginning of the identified packet boundary for each transmitter that isbeing monitored. In such a case, a lookup table preferably is used foradjusting the parameter(s) of filter 18, with the actual adjustmentdepending upon how many different time periods 81 (corresponding todifferent monitored transmitters) currently are overlapping. Once again,such a lookup table preferably relies upon the expected statisticaldistribution of such multiple transmitters transitioning from transmitto no-transmit and vice versa.

In any of the foregoing cases, there typically still will be discretechanges in the received signal power that are due to one or moretransmitters starting to transmit after at least one silent data-packetinterval and/or stopping transmission after at least one data-packetinterval during which a data packet was transmitted. Accordingly, insuch cases the gain profile 100 of FIGS. 6 and 8 will be modified so asto show transitions between any of three or more different power levels(with the actual number of different potential power levelscorresponding to the number of transmitters being monitored), ratherthan transitions between only two different power levels (as actuallyshown in FIGS. 6 and 8).

System Environment

Generally speaking, all of the systems, methods and techniques describedherein can be practiced with the use of a general-purpose computersystem. Such a computer typically will include, for example, at leastsome of the following components interconnected with each other, e.g.,via a common bus: one or more central processing units (CPUs); read-onlymemory (ROM); random access memory (RAM); input/output software,circuitry for both for interfacing with other devices (e.g., using ahardwired connection, such as a serial port, a parallel port, a USBconnection or a firewire connection, or using a wireless protocol, suchas Bluetooth or a 802.11 protocol) and for connecting to one or morenetworks (e.g., using a hardwired connection such as an Ethernet card ora wireless protocol, such as code division multiple access (CDMA),global system for mobile communications (GSM), Bluetooth, a 802.11protocol, or any other cellular-based or non-cellular-based system),which networks, in turn, in many embodiments of the invention, connectto the Internet or to any other networks); a display (such as a cathoderay tube display, a liquid crystal display, an organic light-emittingdisplay, a polymeric light-emitting display or any other thin-filmdisplay); other output devices (such as one or more speakers, aheadphone set and a printer); one or more input devices (such as amouse, touchpad, tablet, touch-sensitive display or other pointingdevice, a keyboard, a keypad, a microphone and a scanner); a massstorage unit (such as a hard disk drive); a real-time clock; a removablestorage read/write device (such as for reading from and writing to RAM,a magnetic disk, a magnetic tape, an opto-magnetic disk, an opticaldisk, or the like); and a modem (e.g., for sending faxes or forconnecting to the Internet or to any other computer network via adial-up connection). In operation, the process steps to implement theabove methods and functionality, to the extent performed by such ageneral-purpose computer, typically initially are stored in mass storage(e.g., the hard disk), are downloaded into RAM and then are executed bythe CPU out of RAM.

Suitable computers for use in implementing the present invention may beobtained from various vendors. Various types of computers may be useddepending upon the size and complexity of the tasks. Suitable computersinclude mainframe computers, multiprocessor computers, workstations,personal computers, and even smaller computers such as PDAs, wirelesstelephones or any other appliance or device, whether stand-alone,hard-wired into a network or wirelessly connected to a network.

In addition, although a general-purpose computer system has beendescribed above, in alternate embodiments a special-purpose processor orcomputer instead (or in addition) is used. In general, any of thefunctionality described above can be implemented in software, hardware,firmware or any combination of these, with the particular implementationbeing selected based on known engineering tradeoffs. In this regard, itis noted that the functionality described above is implemented throughfixed logical steps and therefore can be accomplished throughprogramming (e.g., software or firmware), an appropriate arrangement oflogic components (hardware) or any combination of the two, as iswell-known in the art.

In one representative embodiment of the invention, all of the relevantcomponents and the functionality described above are implemented indigital circuitry. In a somewhat modified embodiment, all of suchcomponents and functionality other than the variable-gain component 14are implemented in digital circuitry, and the variable-gain component 14is an analog amplifier and/or attenuator, with its output beingconverted by an analog-to-digital converter (not shown) into a digitalsignal for processing in modules 16, 20 and 37.

It should be understood that the present invention also relates tomachine-readable media on which are stored program instructions forperforming the methods and functionality of this invention. Such mediainclude, by way of example, magnetic disks, magnetic tape, opticallyreadable media such as CD ROMs and DVD ROMs, or semiconductor memorysuch as PCMCIA cards, USB memory devices, etc. In each case, the mediummay take the form of a portable item such as a small disk, diskette,cassette, etc., or it may take the form of a relatively larger orimmobile item such as a hard disk drive, ROM or RAM provided in acomputer.

The foregoing description primarily emphasizes electronic computers.However, it should be understood that any other type of computer insteadmay be used, such as a computer utilizing any combination of electronic,optical, biological and chemical processing.

Additional Considerations

Several different embodiments of the present invention are describedabove, with each such embodiment described as including certainfeatures. However, it is intended that the features described inconnection with the discussion of any single embodiment are not limitedto that embodiment but may be included and/or arranged in variouscombinations in any of the other embodiments as well, as will beunderstood by those skilled in the art.

Similarly, in the discussion above, functionality sometimes is ascribedto a particular module or component. However, functionality generallymay be redistributed as desired among any different modules orcomponents, in some cases completely obviating the need for a particularcomponent or module and/or requiring the addition of new components ormodules. The precise distribution of functionality preferably is madeaccording to known engineering tradeoffs, with reference to the specificembodiment of the invention, as will be understood by those skilled inthe art.

Thus, although the present invention has been described in detail withregard to the exemplary embodiments thereof and accompanying drawings,it should be apparent to those skilled in the art that variousadaptations and modifications of the present invention may beaccomplished without departing from the spirit and the scope of theinvention. Accordingly, the invention is not limited to the preciseembodiments shown in the drawings and described above. Rather, it isintended that all such variations not departing from the spirit of theinvention be considered as within the scope thereof as limited solely bythe claims appended hereto.

1. A method of controlling gain in a signal receiver, comprising: (a)applying a specified gain to an incoming signal, thereby providing again-adjusted signal; (b) measuring strength of the gain-adjustedsignal; (c) generating a control signal by filtering a signal that isbased on the strength of the gain-adjusted signal; (d) controlling thespecified gain based on the control signal; (e) processing thegain-adjusted signal to identify information regarding data-packetboundaries; and (f) altering a parameter of the filtering in step (c)based on the information regarding data-packet boundaries.
 2. A methodaccording to claim 1, wherein said altering step (f) comprisestemporarily changing a bandwidth of the filtering within a vicinity ofthe data-packet boundaries.
 3. A method according to claim 2, whereinthe bandwidth of the filtering is temporarily increased within thevicinity of the data-packet boundaries.
 4. A method according to claim3, wherein both an amount of increase in the bandwidth and a duration ofthe increase are fixed in advance at constant values for all of thedata-packet boundaries.
 5. A method according to claim 3, wherein thecontrol signal represents a comparison of the strength of thegain-adjusted signal to a target signal strength, wherein a duration ofthe increase is a fraction of a data packet interval, and wherein theincrease in the bandwidth is sufficient to achieve the target signalstrength in response to a transmission boundary by completion of theduration of the increase.
 6. A method according to claim 1, wherein theincoming signal is synchronous.
 7. A method according to claim 1,wherein the parameter of the filtering is altered in step (f) based onan expectation regarding behaviors of plural different transmitters. 8.A method according to claim 1, wherein the altering step (f) is based onidentified data-packet boundaries that are different for each of pluraldifferent transmitters.
 9. A method according to claim 1, wherein thecontrol signal represents a comparison of the strength of thegain-adjusted signal to a target signal strength.
 10. A method accordingto claim 1, wherein the incoming signal has been received across acommunication channel.
 11. An apparatus for controlling gain in a signalreceiver, comprising components configured to: (a) a variable-gaincomponent that receives and applies a specified gain to an incomingsignal, thereby providing a gain-adjusted signal; (b) a detector coupledto an output of the variable-gain component that measures strength ofthe gain-adjusted signal; (c) a filter, coupled to an output of thedetector, that generates a control signal by filtering a signal that isbased on the strength of the gain-adjusted signal, wherein the specifiedgain is controlled based on the control signal; and (d) asignal-processing section that processes the gain-adjusted signal toidentify information regarding data-packet boundaries; and (e) anadjustment module, coupled to the signal-processing section, that altersa parameter of the filter based on the information regarding data-packetboundaries.
 12. An apparatus according to claim 11, wherein saidadjustment module temporarily changes a bandwidth of the filteringwithin a vicinity of the data-packet boundaries.
 13. An apparatusaccording to claim 12, wherein the bandwidth of the filtering istemporarily increased within the vicinity of the data-packet boundaries.14. An apparatus according to claim 13, wherein both an amount ofincrease in the bandwidth and a duration of the increase are fixed inadvance at constant values for all of the data-packet boundaries.
 15. Anapparatus according to claim 13, wherein the control signal represents acomparison of the strength of the gain-adjusted signal to a targetsignal strength, wherein a duration of the increase is a fraction of adata packet interval, and wherein the increase in the bandwidth issufficient to achieve the target signal strength in response to atransmission boundary by completion of the duration of the increase. 16.An apparatus according to claim 11, wherein the incoming signal issynchronous.
 17. An apparatus according to claim 11, wherein theparameter of the filtering is altered by said adjustment module based onan expectation regarding behaviors of plural different transmitters. 18.An apparatus according to claim 11, wherein the parameter of thefiltering is altered by said adjustment module based on identifieddata-packet boundaries that are different for each of plural differenttransmitters.
 19. An apparatus according to claim 11, wherein thecontrol signal represents a comparison of the strength of thegain-adjusted signal to a target signal strength.
 20. An apparatusaccording to claim 11, wherein the incoming signal has been receivedacross a communication channel.
 21. An apparatus for controlling gain ina signal receiver, comprising: (a) means for applying a specified gainto an incoming signal, thereby providing a gain-adjusted signal; (b)means for measuring strength of the gain-adjusted signal; (c) means forgenerating a control signal by filtering a signal that is based on thestrength of the gain-adjusted signal; (d) means for controlling thespecified gain based on the control signal; (e) means for processing thegain-adjusted signal to identify information regarding data-packetboundaries; and (f) means for altering a parameter of the filtering bysaid means (c) based on the information regarding data-packetboundaries.